Peripheral Sensor Interface for Automotive Applications

Transcription

1 I Peripheral Sensor Interface for Automotive Applications Substandard Airbag

2 II Contents 1 Introduction 1 2 Recommended Operation Modes Daisy Chain Operation Principle Preferred Daisy-Chain Mode (#1) : Parallel Initialization Phase Alternative implementation (#2) : Serial Initialization-phase Recommendations for Daisy-Chain application Sensor to ECU communication Scaling of Data Range ECU to Sensor (bidirectional) communication 6 5 Application Layer Implementations Daisy Chain Implementation Sensor start up and Initialization Physical Layer - Parameter and timings System Parameters Timings P10P-500/3L Mode P10P-500/4H Mode Undervoltage Reset and Microcut Rejection Data Transmission Parameters Document History & Modifications 13

3 1 / 13 1 Introduction The substandard Airbag is effective with the Base standard and is valid for all airbag components. It is in full compliance to the previous standard V1.3. It substantiates the base standard with the proposed operation modes and frames formats for all sensors and transceivers used in Airbag applications. Please be aware, that not every feature can be combined among one other. Hence it is in responsibility of the system vendor to evaluate which feature is necessary to fulfill the system requirements and assure that the combination of features is compatible. The document is structured similar to the Base Standard: Chapter 2 gives recommended operation modes, whereas Chapter 3 and 4 define details of the Sensor to ECU, or the ECU to sensor communication, respectively. Chapter 5 describes Application Layer Implementations and in chapter 6 specific system parameters and timings for airbag applications are given.

4 2 / Recommended Operation Modes Asynchronous Operation Mode Sensor Data Description A10P 250/1L min. 1 value each 250µs (incl. tolerances) A16CRC 500/1L min. 1 value each 500µs (incl. tolerances) Synchronous Operation Bus Mode Sensor Data Description P10P 250/1L Single sensor 4kHz data transmission P10P 500/2L Two message slot parallel bus / 500µs data rate P10P 500/3L Three message slot parallel bus / 500µs data rate P10P 500/4H Four message slot parallel bus / 500µs data rate P16CRC 500/2L Two high resolution sensors parallel bus / 500µs data rate D10P 500/3L Three message slot Daisy Chain bus / 500µs data rate D10P 500/4H Four message slot Daisy Chain bus / 500µs data rate Table 1 Recommended operation modes for airbag applications 2.1 Daisy Chain Operation Principle The purpose of the following recommendations is twofold: 1. To narrow down the number of different - or not compatible - Daisy-Chain implementations that could have become available through the various devices (transceivers or sensors) provided by the IC vendors. 2. To ensure that the different implementations are fairly similar, in order to allow application teams to integrate and/or substitute the different Daisy Chain devices into their systems with a reasonable amount of design and validation effort. The different Daisy-Chain solutions can essentially be distinguished by their principle of operation - initialization sequence sent in parallel or sent in series as well as by : Their capability to support one (or several) of the following communication bit rate(s) : o D10P-500/3L : 125 kb/s, 3 time slots maximum o D10P-500/4H : 189 kb/s, 4 time slots maximum The address encoding scheme used for the sensor response (acknowledgement for a successful address setting) The handling of the line switch closure by the sensor : o automatic switch closure along with the address setting (upon first sync pulse after completion of address setting) or 34 o switch closure through dedicated bi-directional instruction (optional) It is therefore recommended that future Daisy-Chain implementations comply with one of the operation modes outlined in the next 2 sub sections.

5 3 / Preferred Daisy-Chain Mode (#1) : Parallel Initialization Phase In this operation mode, each sensor sends out the initialization sequence over the previously assigned sensor time slot. The timeslot is assigned by an address setting instruction. The ECU shall assign the addresses in reverse order, i.e. that timeslot TS1 is the last one receiving its address. Furthermore, timeslot TS1 is defined as being the default timeslot for sensor error reporting in case of an unsuccessful address assignment Principle of operation 1. ECU applies supply voltage to Interface (power on) 2. Wait for supply settling time 3. ECU assigns sensor address for time slot TSi to the next sensor that has not yet received its configuration 4. Addressed sensor responds by sending its internal status (acknowledge or error) message and address confirmation. Sensor closes daisy-chain switch to supply next sensor. 5. Repeat steps 2, 3 and 4 until all sensor addresses have been successfully assigned (From TSn down to TS1) 6. ECU to send RUN broadcast instruction to start runtime mode 7. All sensors to send out their initialization data within their assigned timeslot 8. All sensors to send out sensor_ok messages 9. All sensors to send out their sensor data Bus configuration (Example with 4 time slots) : ECU Figure 1 Bus configuration for operation mode #1 Bus timing for daisy chain mode #1 : TS1 TS2 TS3 TS4 S4 S3 S2 S1 Err_no@ Err_no@ Err_no@ R ACK Init_1 OK ACK, R ACK Init_2 R ACK Init_3 OK @1 ACK Init_4 OK Run_4 Figure 2 Bus timing for operation mode #1

6 4 / Alternative implementation (#2) : Serial Initialization-phase In this operation mode,, each sensor sends out the initialization sequence over the default sensor time slot, right after it is powered on. The timeslot is assigned by an address setting instruction that is sent only once the initialization sequence is over Principle of operation 1. ECU applies supply voltage to Interface (power on) 2. Sensor sends out initialization sequence and sensor_ok messages 3. ECU reads out complete initialization sequence and then assigns sensor address for timeslot TSi 4. Sensor responds by internal status (acknowledge or error) message and address confirmation. Sensor closes daisy-chain switch to supply next sensor. 5. Repeat steps 2 to 5 until all sensor addresses have been successfully assigned. 6. ECU to send RUN broadcast instruction 7. All sensors to send out their Ack 8. All sensors to send out their sensor data Bus configuration (Example with 3 time slots) : ECU Figure 3 Bus configuration for operation mode #2 Bus timing for daisy chain mode #2 : TS1 TS2 TS3 S3 @1 R Init_3 OK ACK,@3 Init_2 OK ACK,@2 Init_1 OK ACK,@1 Ack R R Ack Run_3 Figure 4 Bus timing for operation mode #2

7 5 / Recommendations for Daisy-Chain application Daisy-Chain mode #1 (Section 8.1) is the preferred solution and is recommended for all future circuit designs. It has some significant advantages like a shorter overall initialization duration and the possibility to assess the quality of the communication channel in the assigned slot over the whole initialization sequence (i.e. increased safety for airbag system). Daisy-Chain mode #2 (Section 8.2) is included here because it has already been designed into several sensors and might therefore be used as well in some applications. Any further operation mode should - in principle - be avoided in order to avoid unnecessary diversity Sensor to ECU communication Basically the full data range as specified within the Base can be applied to. Recommended Data word length is a 10 bit data word (payload) with two start bits and one Parity bit for error detection. 3.1 Scaling of Data Range For sensors with a data word length of more than 10 bit, the data range scales as described in the V2.0 Base. Furthermore, the following definition is effective: status and initialization data words of range 2 and 3 are filled up with the value of the bit corresponding to the D0 bit in the 10 Bit data word (possibility to check for stuck bits in the receiver). Mapping of Status & Initialization Data 16 Bit Data Word 10 Bit Data Word Example Block ID 16 0x20F D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D D9 D8 D7 D6 D5 D4 D3 D2 D1 D F Figure 5 Mapping of status and initialization data into a data word

8 6 / 13 value Signification Dec Hex x7FFF Reserved (ECU internal use) Range x79FF Sensor Ready : : x7800 Maximum Sensor Data Value : : : 0 0x0000 : : : x8800 Minimum Sensor Data Value x87FF Status Data 1111 : : : x8400 Status Data x83FF Block ID 16 : : : x8000 Block ID 1 Table 2 Scaling example: Data Range for a 16 Bit data frame 4 ECU to Sensor (bidirectional) communication Status & Error Messages Sensor Output Signal Block ID's and Data for Initialisation ECU to Sensor communication is executed in Tooth gap mode as defined in the base standard. Sensor response during bidirectional communication is carried out in Data range codes RC, RD1 and RD

9 7 / 13 5 Application Layer Implementations Daisy Chain Implementation List of messages : ECU to sensor (short instructions) : [@1] = 0x28CE Set address #1 [@2] = 0x28AF Set address #2 [@3] = 0x28E8 Set address #3 [@4] = 0x289A Set address #4 [R] = 0x2F8F Run Sensor to ECU : Err_no@ : Sensor error code when address assignment was not successful Sensor address = RD1 = encoded values from data range 3 = = = = 0x214) Note : following messages are used in the drawings, but are not specific to daisy chain applications Ack = RC = 0x1E1 (or Err = 0x1E2) OK = 0x1E7 5.2 Sensor start up and Initialization Sensor identification data is sent via Data Range Initialization. The initialization phase is divided into three phases and the data message repetition count k typically has a value of 4. Start-Up and Initialization Initialization Phase I No Data Transmission Initialization Phase II Transmission of Type Code & Serial N Sensor Self Test Initialization Phase III Transmission of "sensor ready", "sensor defect" or other sensor specific data Run Mode Transmission of sensor or status data t = 0 t INIT1 t INIT2 t INIT3 Transmission of Initialization Data ID1 D1 ID1 D1 ID1 D1 k * (IDn + Dn) ID2 D2 Figure 6 Initialization phases of the sensor

10 8 / 13 Figure 7 Duration of initialization phases Initialisation Phase I t = ms Typical: 100 ms Duration of the initialization phases Initialisation Phase III Minimum: 2 messages Maximum: 200 ms Typical: 10 values Initialization Data Content: The following definitions are made in addition to the Base. Mandatory definitions: Head Initialization Vendor ID Product ID Data field F1 F2 F3 F4 F5 Data nibble D1 D2 D3 D4 D5 D6 D7 D8 D9 Recommended definitions: v. # of Datablocks Vendor ID Sensor type Sensor param. Application specific Data field F6 F7 F8 F9 Data nibble D10 D11 D12 D13 D14 D15 D16 D17 D18 D19... D32 Sensor manuf. Sensor application Sensor production date Sensor trace inf. Field Name Parameter definition Value F1 (D1) F2 (D2, D3) F3 (D4, D5) F4 (D6, D7) Meta Information (See footnote below) Initialization data Length Number of Data nibbles transmitted Protocol Description (D1) x, Data Range Initialization Example: F1-F9 Vendor ID s. Base Ch Sensor Type Definition of the sensor type (acceleration, pressure, temperature, torque, force, angle, etc.) Acceleration Sensor (High g) Acceleration Sensor (Low g) Pressure Sensor other sensors Example: XXXX 0001 XXXX 0010 XXXX 1000 tbd F5 (D8,D9) Sensor Parameter Definition of sensor specific parameters e.g. measurement range. Information depending on the corresponding sensor type Sensor specific definition F6 (D10,D11) Sensor Code (Sensor manufacturer) Definition of sensor specific parameters or additional information. To be specified by the sensor manufacturer. Sensor specific definition F7 (D12-D14) Sensor Code (Sensor application) Usage e.g. for product revision information. Sensor specific definition

11 9 / 13 F8 (D15-D18) Sensor Production Date Production date of the sensor. Binary coded julian date: Year: (7 bit value) Example: 2006: Month: (4 bit value) March: 0011 Day: (5 bit value) 30: F9 (D19-D32) Sensor Trace information E.g. production lot / line / serial number To be specified by the sensor manufacturer Sensor specific definition 114 Table 3 Initialization data content Note : For compatibility reasons with legacy airbag applications, the field F1 (D1) should refer to ver 1.3, value = For upcoming sensors - compliant with ver 2.x - it is recommended to have the F1 (D1) value configurable to either 0110 or 0100 depending on application needs. 118

12 10 / Physical Layer - Parameter and timings System Parameters Airbag systems are implemented in Common Mode with the following selected parameters Common Mode Supply Voltage (standard mode); V CE, min = 5.5V; V SS, min = 5.0V Supply Voltage (increased mode); V CE, min = 6.5V; V SS, min = 5.0V Sync signal sustain voltage V t2 = 3.5V Internal ECU Resistance R E, max = Timings Please note that due to backward compatibility the values given below are adopted from V1.3. Derivations to calculated timeslots according to Ch. 6.6 in the V2.0 Base Standard are possible P10P-500/3L Mode This example is calculated with a standard sensor clock tolerance of 5%. N Parameter Symbol Remark min nom max Unit 1 Sync signal period T Sync µs Maximum tolerance of sync signal period +/-1 t N Ex t N Nx t N Lx 2 Slot 1 start time t 1 xs Related to t 0 44 µs 3 Slot 1 end time t 1 xe Related to t 0 µs 4 Slot 2 start time t 2 xs Related to t µs 5 Slot 2 end time t 2 xe Related to t 0 µs 6 Slot 3 start time t 3 xs Related to t µs 7 Slot 3 end time t 3 xe Related to t µs Table 4 -P10P-500/3L timeslots specification The timings also apply for universal bus mode and daisy chain bus mode.

13 11 / P10P-500/4H Mode This example is calculated with a standard sensor clock tolerance of 5%. N Parameter Symbol Remark min nom max Unit 1 Sync signal period T Sync µs Maximum tolerance of sync signal period +/-1 t N Ex t N Nx t N Lx 2 Slot 1 start time t 1 xs Related to t 0 44 µs 3 Slot 1 end time t 1 xe Related to t 0 µs 4 Slot 2 start time t 2 xs Related to t µs 5 Slot 2 end time t 2 xe Related to t 0 µs 6 Slot 3 start time t 3 xs Related to t µs Slot 3 end time t 3 xe Related to t 0 µs 8 Slot 4 start time t 4 xs Related to t µs 9 Slot 4 end time t 4 xe Related to t µs Table 5 -P10P-500/4H timeslots specification The timings also apply for universal bus mode and daisy chain bus mode. 6.3 Undervoltage Reset and Microcut Rejection The sensor must perform an internal reset if the supply voltage drops below a certain threshold for a specified time. By applying such a voltage drop, the ECU is able to initiate a safe reset of all attached sensors. Microcuts might be caused by lose wires or connectors. Microcuts within the specified limits shall not lead to a malfunction or degraded performance of the sensor. V V Th, max / V SS, min Normal Operation undefined V Th, min I S =0 Reset 0 0.5µs 5ms t Figure 8 Undervoltage reset behaviour

14 12 / 13 N Parameter Symbol/Remark Min Typ Max Unit 1 Undervoltage reset threshold V Th - standard voltage mode 3 5 V (V Th, min = must reset; V Th, max = V SS, min ) 2 Time below threshold for the sensor to initiate a reset 3 Microcut rejection time (no sensor reset t Th 5 ms I S =0 0.5 µs allowed) : standard 4* Microcut rejection time (no sensor reset allowed) : optional I S =0 Applicable test conditions for this specification : micro-cuts of 10 µs, applied every 1 ms 10 µs for a total duration of 4 s Table 6 Undervoltage reset specification 4*) Note: as the micro-cut duration of 10 µs exceeds the transmission bit time, data frame [or sync pulse] corruption might occur when the micro-cut is applied. So it cannot be guaranteed that all data frames are successfully transmitted, but a reset of the sensor (with a complete initialization sequence sent out) is not allowed. The voltage V Th is at the pins of the sensors. In case of microcuts (I S =0) to a maximum duration of 0.5µs (Optional 10 µs) the sensor must not perform a reset. If the voltage at the pins of the sensor remains above V TH the sensor must not perform a reset. If the voltage at the pins of the sensor falls below 3V for more than 5ms the sensor has to perform a reset. Different definitions may apply for Universal Bus and Daisy Chain Bus. 6.4 Data Transmission Parameters N Parameter Symbol/Remark Min Typ Max Unit 3* Sensor clock deviation during data frame 0.1 % Table 7 Data transmission parameters for airbag applications maximum temperature gradient and maximum frame length

15 13 / Document History & Modifications Rev.N Chapter Description / Changes Date 2.0 all First Release of Airbag Substandard; Revision Number of corresponding Base Document adopted Add Daisy Chain modes in table of section 2 (Recommended operation modes) Add chapter 2.1, on guidelines for implementation of daisy chain operation modes Editorial Changes Single decimal codes in table 1 corrected 5.1 new 6.3 new Add switch closure time (1 st sync pulse after address setting) switch closure through dedicated bi-directional instruction => optional 2.1 all Some minor changes : add captions for figures and tables 3.1 Signal amplitude 0 => If symmetrical sensor scale 2 A8P mode has been deleted from table 1. covers only 10bit+ data sizes 3.1 Removed : Signal amplitude 0 for 0x0000 value in table Add note for clarification of the list of messages from sensor to ECU : ACK & OK not specific to daisy chain mode 5.2 Changed ver 2.0 to ver 2.x in footnote of table 3, as note is applicable for all upcoming versions 6 Add footnote to table 6 for clarification of sensor reset behavior when micro-cuts are applied 6.1 Add increased voltage mode for daisy chain applications : V CE min = 6.5 V 6.4 Add section 6.4 : Data Transmission Parameters Add Sensor clock deviation during data frame : 0.1 % max (Table 7)